Output



March 3, 1959 v K HAYNES Re. 24,614

MAGNETIC CORE LOGICAL cmcun's Original Filed July 30, 1953 3 B I -H +H +H V 1' .t z ,4

d Au Ideol hysteresis loop ---Actual hysteresis loop OUTPUT b OUTPUT Y INVEN TOR.

MUNRO K. HAYNES United States Patent O MAGNETIC CORE LOGICAL CIRCUITS Munro K. Haynes, Dutchess County, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York No. 2,695,993, dated November 30, 1954, Serial No. 371,239, July 30, 1953. Application for reissue May 4, 1955, Serial No. 506,101

17 Claims. (Cl. 340-174 Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

This invention relates to pulse transfer circuits and more particularly to circuits which are adapted to perform logical operations on binary digits.

Logical circuits are employed throughout accounting equipment and computers for widely different purposes and are variously known as gates, buffers, coincidence circuits and the like. This invention is directed to a particular type of logical circuit termed an exclusive or circuit. Such a circuit is one having a plurality of input terminals and a single output terminal at which a pulse is produced when a pulse is applied to one and only one of the input terminals. Considering a circuit with two input terminals, then no output pulse is produced when both input terminals receive pulses or when neither receive input pulses.

Electronic computers employ a large number of vacuum tubes and, while such tubes may have long life individually, where large. numbers are employed, the likelihood offailure of one tube is quite great. In many instances, the failure of only a single tube may completely disable the unit and as a consequence, there has been a trend in computer research generally to replace vacuum tube circuits with components which are more reliable, have longer life and are more economical.

Accordingly, it is an object of my invention to provide an exclusive or logical circuit which is more economical, uses fewer elements and is more reliable in operation than comparable circuits using vacuum tubes.

' A more specific objectof this invention is to provide an exclusive or circuit utilizing magnetic binary elements for performing logical operations.

Another object of the invention is to provide an improved exclusive or circuit having negligible power consumption and requiring only low voltage bias sources for operation.

Still another object is to provide an exclusive or circuit utilizing magnetic elements which is capable of storing binary information in addition to performance of the logical circuit operation.

Another object of the invention is to provide an exclusive or circuit adapted to receive input pulses over a selectable time interval and to produce an output indication at a selectable time,

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. 1 is a diagram of an actualand ideal hysteresis loop for core material used in a magnetic binary element.

Fig. 2 is. a schematic representation of an exclusive or circuit utilizing two bistable magnetic cores.

the coercive force -H causes the core to traverse its.

'resentative of a binary zero.

-- is induced in the secondary windings.

-- and 2 are illustrated, each having four windings.

. ings.

Re. 24,614 Reissued 53 9 Fig. 3 is a schematic illustration of another form of circuit embodying the invention.

Fig. 4 illustrates still another embodiment of the invention in which transistors are employed.

Magnetic material having the property of low coercive force and high residual magnetism may be readily magnetized in one direction or one remanence state representative of a binary one and in the opposite staferep- A core fabricated of such materials may be placed in one of these two states of remanence by means of windings on the core to which pulses are applied, and the particular state existing within a core may be determined by a voltage pulse induced in other windings on the core when the flux state is reversed. An ideal core material for this purpose would have a substantially rectangular hysteresis loop such as that illustrated in Fig. 1. With the binary zero state arbitrarily selected'as point a on the curve application 'of a positive magnetizing force H sutficiently greater than the coercive force +H will cause 1 the corejto traverse the hysteresis loop to saturation point b,;,and, on removal of the applied magnetomotive force, returns. to point c which represents a binary one state. Similarly, when in a one remanence state, application of a negative magnetizing force H sufliciently greater than hysteresis loop from point e to point d and, on re-, m-oval, to point a. The change in flux when the core is caused to go from the one" state to the,zero;st'ate or from the zero state to the one state, induces an output voltage pulse in each of the windings on the core, however, application of a magnetomotive force tending to maintain the core in either existing remanence state would ideally produceno flux changeand consequentially, no output pulse would be produced. Due to the fact that core materials do not possess perfectly rectangular hysteresis loops, there is a flux change, for example, as the core goes from its stable negative remanence state of a read-out pulse, and a voltage of. reduced magnitude Provision is, therefore, made for discriminating between output pulses reduced on readin out from a zero remanence state' and on reading out from a one remanence state.

Referring now to Fig. 2, two bistable magnetic cores 1 A dot is placed at one end of each of these windings 'to indicate that that end has a negative polarityduring read-in of a binary one and a positive polarity during read-out placed near the windings in other schematic views. 7

of a binary one. Similar dots are Core 1 is provided with an input winding 3, read-out winding 4 and output windings 5 and 6. Core 2 is simi larly provided with an input winding 7, read-out winding 8 and output windings 9 and 10. Input windings 3'and 7 are grounded at one end and the remaining ends com-' prise input terminals to which pulses X and Y respectively, are applied. Windings 4 and 8 are connected in series and are simultaneously pulsed during read-out by'application of potential from a source (not shownyto terminals 11 and 12. Other circuit arrangements for pulsing the read-out windings simultaneously maybe employed and parallel coupling of windings 4and 8 is contemplated. The output windings 5 and 9 are connected in series with a diode 13 and windings (Hand 10 are con nected in series with a diode 14. These two series branches are connected in parallel, with one junction or this parallel circuit coupled to the negative terminal'of a voltage source 15 and the diodes 13 and -.14 poled to through th'e wind-j The other junction of these paralleled branches" prevent current flow from this source is connected to an output terminal 16 and to one tera to its negative saturation state d, during application] g state to the saturation state (point a to n f in F .1 A tsr t X dn Pu e es, the'j core' 1 returns to and remains in the stable rrnanence' state (pointc of Fig. 1) and a binary a ts ed nw The'flun change caused by the X read-in pulse causes a voltage to beindueed eachof the windings 4, 5 and E6 d hs'a l nty 9 the e nduc d v a s negative at the dot marked ends of these windings. Conng: winding 4, terminals 11 and 12 appear as an rcurterrc'ept' during read-out time and'no current flows through this winding. The polarity of the voltage developed in winding 5 is such that current flow is blocked bytthe' iode 13. However, the polarity of the voltage developeddn winding 6 is such that current flow is in the low"resistance'direction of diode 14 but opposed by the s6urce15. Thenurnberof turns of winding 6 and the potential of source15 are adjusted so that the voltage V of th'lattefbp'poses the voltage induced in Winding 6 to such a'degree that no current or at least a current of only negligible magnitude flows through the load 17 during 'read iri' of the X pulse.

"Core 1" is-now in a one state and core 2 is in a zero-"state as a result of the presence of an X input pulse and "the absence of a Y- input pulse. According t'o 'the" definition heretofore given of an exclusive or circuit, this condition-should produce an output pulse during read-out time.

' Current'is caused to flow through both windings 4 and 8 on read-out and is applied in a direction to'produce a negative magnetizing force H in cores 1 and 2 which is sufficient'tocause them to return to state a (Fig. 1 representing storage of a binary zero. Since core 2 is in a z'ero. storage state, no flux reversal takes place in this core due to read-out current in Winding 8 and'no voltage, ideally, is developed in either of the output Windings 9 and 10. Core 1, however, is storing a binary fone and euergization of winding 4 causes a voltage to be induced in windings 5 and 6. The polarity of the voltage induced in winding 6, as indicated by the dot, is such that current'flow is blocked by the'diode 14. The voltage induced in winding 5, however,'is in such a direction of polarity as to cause current flow through the diode 13 and also through the threshold voltage source 15 in a charging direction. The number of 'turnsof winding 5 are'adjusted so that a" voltage having a range of magnitude between the Values V' and 2V is induced ther in which will result in a voltage having a value between zero and V appearing across load'17v when opposed; by the bias voltage Viof source 15. The current path: for; this induced voltage may be traced from the dot markedend of winding 5, which is positive on reado t 1 t ,'to the, terminal 16, load 17, the positive terminal of the source 15 and, overcoming this bias voltage of magitu e V,. through the diode 13, winding 9 of core 2 and baclt to the negative terminal of winding 5. The voltage drodacross load 17 is substantially the difference between the'in'duced voltage and the bias battery voltage and has lar y. such that the end connected to terminal 16 is i "The actual. voltage developed across th eload e e b the ro r u e l weraueediode 1 3 and an opposing voltage of. induced. in winding 9 on read-out. The the. condition stated,- is in a zero storage e1 uchthat it traverses its hysteresis loop fromstate and, on application of a negative read-out pulse to W n n h s a ne at e ei ens ates terse, else a l ed. causing core 2 to go froin point a" to point (1 Fig; 1). Since the core material doesnot have an ideal rectangular hysteresis loop, there will be a small flux change in going from point a" to point d and a voltage of small magnitude V is, therefore, produced in Winding 9 and has a polarity such as to oppose that induced 'iriwi ndin g 5.

Application of the read-out pulse, therefore, produces an ou'tputpulse which may have a magnitude'sub'stan tially as great as V across load 17, fulfillinga first requirement for an exclusive or logical circuit, and has reset cores 1 and 2, to a binary zero state.

In a similar manner, an output pulse is prOduced on the condition that an input pulse Y is applied to winding 7 and pulse X is not applied to winding 3. In this case, however, the core 2 will store a binary one and application of a read-out pulse to terminals 11 and 12 energizing windings 4 and 8, develops a voltage having a range magnitude between the values V and 2V across Winding 10 and a voltage which may have a magnitude V or greater across winding 9, as determined by the number of turns of these windings. The diode 13 is poled in such a direction that current cannot flow due to the voltage developed in winding 9, however, the voltag v n-v d ed in nd c usss C r e t l w't rou h a. pa traced from the dot marked end of this winding, through W nd n 6 of e Oppo d by an n u e l g V. o he terminal. 6 n throu h lea .U't thes onnded positive side of source 15, thence through the source 15 in a charging direction and through the diode 1 4 to the negative terminal of winding 10. A voltage which may be substantially of magnitude V, depending upon the number of turns of winding 10, thus is developed across load 17 and is of the same polarity as that developed as a result ot the X pulse alone.

on their hysteresis loops (Big- 1).- prl t n e the read-out pulse causes each of'these cores to go from point a to point d and a small voltage will be induced in each of the windings due to this flux change. Winding 5 has a voltage within the range V to 2V de veloped while winding 9 has a voltage as to a value V which opposes that induced, in winding 5, and, since the net induced voltage V isless than the bias source voltage V, no current flo ws through the load 17'. Winding ljlof core Q has a voltage within the range V to 2V developed which is opposed by a VOltag'e, lip-to a, value. Y induced in wind 6 Wm The. e. 'iiidused. tage/iv is .50. s, th g h oppo ing ia vol ag V; f om s urc 1,5. andno current flows through lead r;

In order to satisfy'the rem nswndfl'qg for, anjex s s ve ir ai an Qu rut sl na ms t'not e'p dn esi. f 29th i r j i lsss' a d Y, ar Pr sent- .X. afid Y pulses may be applied simultaneously or atseparat voltage between the values V andZ Vis, induced in wind,- ings 5 and 10L It will be recalled that dot not adjacentthe ends of these windings ir'rdie'ates a neg rye polarity on read-in operations and the, algebraic of the voltages induced in, windings 5 and 9 is such that the, resultant voltage isopposedby the diode 13. Similarly, the algebraic sum'of th'e'voltages induced in windingse and; 10"is such that the" resultant volta e isopposedfby the diode 14." No spurious response, therefore, is produced during simultaneous read-in or in any read in' operation. I T

We have. yet, however, to consider the condition that no. output pulse 'is/to beprodu ced-acr 'oss the load-on read ing out: cores. t and @whenbott arelina one rnianence 7 state as when both X and Y input pulses have received. 1 With the cores in a stored'remanence state (point e of Fig. 1), a read-out pulse now causes a voltage having a magnitude up to the value V to be induced in both winding 6 of core 1 and winding 9 of core 2 and a voltage having a magnitude between the values V and 2V is induced in winding 5 of core 1 and winding of core 2. The algebraic sum of the voltages induced in windings 5 and 9 is applied in the low resistancedirection of diode 13 but is opposed by the threshold bias voltage V of source 15. Likewise the algebraic sum of the voltages developed in windings 6 and 10 is applied in the low resistance direction of diode 14 but is also opposed by the threshold bias voltage V of source 15. Hence, the diodes do not conduct and no current flows through the load 17 and no output is obtained with both X and Y inputs applied.

It will be noted that the voltages induced in windings 6 and 9 during read-in cores 1 and 2 respectively are of been such polarity that current will tend to flow through diode 14 and 13 unless prevented by the threshold bias of source 15. These induced voltages, therefore, are made equal to or less than the bias voltage V in order to prevent the appearance of an output pulse through load 17 during read-in. a

The turns ratio of windings 5 and 10 are adjusted so as to be somewhat greater than that of the windings 6 and 9 up to a ratio of two to one and, during read-in, voltages having a magnitude of 2V or less are developed. The voltage developed in either of these windings when only one input is applied (X or Y pulse) is prevented from flowing through the load 17 by the diodes 13 or 14. Read-in of both X and Y pulses simultaneously causes voltages of 2V or less to be induced in windings 5 and 10 which are opposed to the voltage induced in windings 9 and 6. The resultant voltages of V or less are then blocked by the diodes 14 and 13.

During read-out, the voltages developed in windings 6 and 9 are in opposition to the voltages developedin windings 10 and 5 respectively. With only a single, input pulse previously applied and stored, the opposition is negligible and the 2V or less voltage developed in the winding 10 or 5 is sufficient to produce a pulse of magnitude V or less across the load. With both pulses X and Y stored, the voltages induced in windings 6 and 9 are opposed to the voltages induced in windings 10 and 5 and must result in an algebraic sum equal to or less than the voltage V of the bias source in order to prevent a spurious output voltage across the load 17. It is thus seen that the bias voltage V of source 15 must 'be made equal to or greater than that induced in either winding 6 or 9 on read-in and the more nearly equal these voltages are, the greater the output response obtained. 7

Also, the bias voltage V must be made greater than the resultant voltage induced in windings 5 and 9 and the resultant voltage induced in windings 10 and 6 on readout. In other words, for maximum output signal, the voltages developed in windings 6 and 9 are desirably less onread-in and greater on read-out as compared with the fixed voltage V. This may be accomplished by adjusting the number of turns of the read-in and read-out windings or by using a read-in pulse of lower driving power than the read-out pulse since the time rate of flux change, and consequently the voltage developed,is dependent upon the driving power. i

It is thus seen that the circuit of Fig. 2 meets all the requirements of an exclusive or circuit and, as the read-out pulses may be applied at any selected time interval, after read-in is completed, this circuit is also capable of storing binary information in addition to performing the logical operation.

Referring to the modification illustrated in Fig. 3, two loads labelled 18 and 19 are employed with windings 5 and 9 connected in series with load 19 and windings 10 and 6 connected in series with load 18.; In this manner, the circuit of Fig. 3 is capable 'of indicating if the. input X-alone, or input.Y.alone, had. beenpreviously stored. Read-outof only an X input pulse develops a voltage of V or less across load 19 while read-out of only a Y input pulse develops a voltage V or less across-load 18;

The bias voltage V as represented by the battery 15 in both Figures 2 and 3 may be supplied by any equivalent voltage source acting in continuous opposition to ,the diodes 13 and '14 and providing a reliable threshold voltage which must be exceeded by some. predetermined amount in order to produce a significant currentflow through the load 17 or loads 18 and 19., The battery; symbol employed isv intended to. represent any source of steady bias voltage having a low internal impedance.- It should be noted thatthe source 15 does not furnish any power and 'may thus be employed .to supply bias potential for a large number of circuits such as that shown.

Figure 4 illustrates a circuit adapted to store binary information and perform logical operations similar to the foregoing embodiments except that in this instance the threshold voltage is maintained germaniurnftranr sistors 20 ,and 21 or other semi-conductor amplifiers. Emitters 22 and 23 are biased by fixed voltage sources Ex and Ey respectively with emitter 22 and base 24 of transistor 20 connected in series with source By and the windings 6 -and.10.- The positive terminal-of source By and a second voltage sourced? are grounded and the negative terminal of-the latter is connected through load 17-to collector 25 of -transistor 2l l. The connections for,

transistor 21 and windings 5 and 9 with the sourcesEx and P and with the load 17 are made in a similar manneras described for the transistor 20 and windings 6 and 10.

Considering read-in of an X pulse, a voltage is induced in winding 5 in a direction additive to the biasof source Ex, and emitter 23 is made rnore negative with respect" to base 26 so that. no conduction takes place. A voltage is induced also in, winding 6 which is insufiicienttoovercome the bias: source Eyand transistor .20-does not.

conduct.

Reading in both an .X and Y.pulse simultaneously inlduces voltages inwindings 5, 6, 9 and 10 such that the. emitters 22 and 23 are biased more, negatively and-conduction does not occur.

Reading out a stored X pulse, according to the defini tion heretofore made of an exclusive or circuit, willproducean output pulse through load,17. ,In this case,;a.'

voltage is induced in winding 5 which is in a direction to overcome the bias of sourceEx andthe, emitter 232i$ raised in potential with respect to base 26 and-conduction takes place between base 26 and collector-27. Power is now supplied from. the source P during the read-outginterval and flowsthroughwwinding 1 7. :Little poweris consumed, however, due to the; amplification oftran: sister 21. 1 l

.Read-out of a stored Y-pulse operates in a similar ages induced in windings 6 and 10 are-oppo'sedwith thenet voltage equal to or less than the b'iasvoltage of source By so that transistor 20 does not conduct and the voltages induced in windings .5 and 9 are in opposition with the net voltage less than or equal to the bias voltage of source Ex so that transistor 21 doesnotconduct. L

v It is evident that electron tubes can be used to establishand maintain a reliable threshold voltage for discriniinating between pulses of variable 'magnitude, however, cry's tal diodes as shown inj'Fig'ures Z andfEl transistors as 7 time 29W?! e u L n IPl h twice for h i ease wn an dsssr hsd. and

99!! 19W was;

e Ps t il si 'fth i aa msfita Pfl s ease 9 e i vsntisa s pg sd f6 ste red emb d h m t w ll be undersmd?! hat si g i sw s' ns' an ubst fien and h -1 s i h is!!! sad deta ls 6f e d ic ill t as? in s rs s may 2 mad by es ki led n the art-withoutide ing from the spirit of the invention.

theint K on therefore, to be limited only as indicatedby the scope of the following claims.

l. {in "exclus veor" logical circuit comprising at least two m ss s? st rage snvs it v sas clud n re of magnetic 'inatei' l'c'apable of assuming alternate states st s s ab ht ispr ssmat vq o b a and one coqqi on ar s-i? wi sliss 6 e ch. we d p t b P s t says. a, t e itgras elem w su a binary one state, a read-out Winding on each core d pt d to b n t-seq for wetti h st rage men to a zero sitatejtirs't and second output windings on each wh s vi ass Pulses a e in u ed in r po to change in the magnetic state oi the storage elem i i, said 'output windi gs having a turns ratio greater than that'ofsaid second windings and wound in opposing directions, circuit ans connecting the first winding on idfirs't sire s w l i'ths wn! w nd on d seeond core and the second winding on said first core in series with the first winding on said second core, fixed bias voltage soutce' means, and coupling said series connected windings in parallel and in series with said fixedbias source and a load, coupling means iniIY "'2. Apparatus as set forth in claim 1 wherein said electrically conductive devices are diodes connected in op-v position to said fixedbias source means.

' '3; Apparatus accordingto claim 1 wherein said electrically'c onductive devices are transistors adapted to pass, an electr'ical pulse only when said storage elements are singly reset to a "zero' binary state from a'one' binary state.

4, An exclusive or circuit comprising first and second magnetic storage devices capable of assuming alternate states of magnetic'stability representative ofzero' and one? binary conditions, read-in means associated with said first device and adapted to cause said first device to' assume a binary one state, read-in means associated withsaid second device and adapted to cause said} second device to'assume a binary one state, readout means associated with said devices and adapted to causesa id devices to assume binary"zero states, first and second output windings associated with each of said devices; fixed bias voltage means, circuit means connecting -t-lie"first w1nding ofsaid first device 'in series with thesecond'windingof the second device and the second winding of said first device in series with the first winding oE-said second'device, and means coupling said series coiinected 'windings andsaid fixed'bias means in series with a load, said coupling means including elements electrically conductive in one direction only.

5. Apparatus according to claim 4, wherein said coupling means cc irn'prises diodes biased by said' source so as to a voltage pulseonly-When said first-andf second devices are singly.- caused to assume a binary *zero state fromia binary. one: state. on application of a current cludingfdevices electrically conductive in' one direction pulsei tosaidrreadouemeans. y v Appatallls according to claim .4,. wherein. said coupling. in, comprises, semi-conducting amplifiers adapted to b saemlec rical; -in1pu .se'onwwhensaid, first;

and seco de se aws sl saus q s ume. bi a y p I my of magnetic o ass'u ej one oftwo tabl ma etic st es m a fa s ssti y cau in said. elements to assume a first stable state, means for resetting said elem t mul nsqus o a c n b sta secondary windings on said elements in which voltages of opposed polarity and different magnitude are induced when the respective storage elements are reset from a first stable state to a second stable state, a voltage responsive load device, means series connecting secondary windings of unlilce polarity and magnitude on at least two of said storage elements, fixed bias voltage means, and circuit means including unidirectional current conducting means connected in opposition to said fixed bias voltage means and coupling said series connected secondary windings in parallel and in series with said load device.

8. Apparatus according to claim 7 wherein said unidirectional current conducting means comprise diodes biased by said voltage means to pass a voltage pulse through said load device only when one of said storage elements is reset from a first to a second stable magnetic state.

9. Apparatus according to claim 8 wherein said unidirectional conducting means comprises semi-conducting amplifiers adapted to pass an electrical impulse only when one of said storage elements is reset from a first to a second stable magnetic state.

10. A logical circuit comprising two magnetic storage elements each adapted to assume one of two stable magnetic states, means for selectively causing said elements to assume a first stable state, means for resetting said elements simultaneously to a second stable state, secondary windings on said elements in which voltages of opposed polarity and different magnitude are induced when the respective storage elements are reset from one to the other stable state, a pair of voltage responsive load devices, means connecting the secondary windings on one core in series with the secondary windings on the other core which are of unlike polarity and magnitude, means including a diode connecting each of said pairs of windings, in series'individually with one of said load devices, and fixed bias means jointly coupling said load devices and said pairs of windings in such a manner that said diodes. prevent current flow through said windings, from said fixed bias source.

11. An exclusive or logical circuit comprising at least two magnetic storage elements, each including a core of magnetic material having alternate states of magnetic stability representative of binary zero and one conditions, a read-in winding on each core adapted to be pulsed for causing the storage element to assume a binary one state, a read-out winding on each core adaptedto he pulsed for resetting the storage element to a zero state, first and second output windings on each core wherein voltage pulses are induced in response to change in the magnetic state of the storage element, said first output windings having a turns ratio approximately twice that of said second windings and wound in opposing directions, circuit means connecting the first winding on said first core in series with the second winding on said'second core and the second winding on said first core in series with the first Winding on said second, core, fixed bias voltage source means, and means coupling said series connected windings in parallel'and in series with said fixed bias source and a load, said coupling means including devices electrically conductive in one direction only.

12. Apparatus as set forth in claim 11 wherein said electrically conductive devices are diodes connected in opposition to said fixed biassource means.

13. Apparatus according to claim 11 wherein said elec- J trically conductive devices are transistors adapted to pass an electrical pulse only when said storage elements are singly reset to a zero binary state from a one binary state.

a 14. A logical circuit comprising two magnetic storage elements each adapted to assume, one of two stable magnetic states, means for selectively causing said elements to assume a first stable state, means of lower driving power for resetting said elements simultaneously to a secand stable state, secondary windings on said elements in which voltages of opposed polarity and different magnitude are induced when the respective storage elements are reset from one to the other stable state, a pair of voltage responsive load devices, means connecting the secondary windings on one core in series with the secondary windings on the other core which are of unlike polarity and magnitude, means including a diode connecting each of said pairs of windings in series individually with one of said load devices, and fixed bias means jointly coupling said load devices and said pairs of windings in such a manner that said diodes prevent current flow through said windings from said fixed bias source.

15. A saturable core exclusive or logical circuit comprising a pair of storage elements each including a core of magnetic material capable of assuming alternate states of magnetic stability, a read-in winding on each core adapted to be pulsed for causing the storage element to assume one magnetic state, a read-out winding on each core adapted to be pulsed for resetting the storage element to the other magnetic state, first and second oppositely poled output windings on each said core wherein voltage pulses are induced in response to a change in the magnetic state of the storage element, circuit means connecting the output windings of said pair of cores in series opposition, and means coupling said series connected pairs of windings in parallel and to a load device for developing an output signal when only one of said cores is reset to the other magnetic state.

16. A saturable core exclusive or logical circuit comprising a pair of storage elements each including a core of magnetic material capable of assuming alternate states of magnetic stability, a read-in winding on each core and individual thereto adapted to be pulsed for causing the storage element to assume one magnetic state, a fead-oui winding on each core adapted to be pulsed for resetting the storage element to the other magnetic state, an output winding on each said core wherein voltage pulses are induced in response to a change in the magnetic state of the storage element, circuit means connecting said output windings in series opposition in series with a load device for developing a unipolar output signal thereacross when only one of said cores is reset to the other magnetic state.

17. An exclusive or logical circuit comprising two magnetic cores capable of assuming alternate states of magnetic stability, first winding means on each of said core and individual thereto for selectively causing one of said stable states to be assumed, second winding means on each said core operable for simultaneously causing each said core to assume the other stable state, third winding means on each said. corewherein a voltage is developed in response to a change from said one to said other stable state on operation of said second winding means, and circuit means connecting said third winding means in series opposition and in series with a load device whereupon an output signal voltage is developed across said load when a given one of said cores is in said other stable state and said second winding means is operated.

References Cited in the file of this patent or the original patent UNITED STATES PATENTS Bennett May 13, 1952 Lo Dec. 7, 1954 OTHER REFERENCES 

